550 
are (@) horizontal strata moving with different 
velocities, (6) columns of air with different ver- 
tical components. The boundary between such 
strata and columns often is quite narrow, and 
hence the aviator may pass with disconcerting 
abruptness from one to the other. On certain 
conditions the downward acceleration may be even 
in excess of that due to gravitation and thus the 
aviator thrown out of his seat. 
Aeronautical Screw Propellers: SPENCER HEATH, 
Washington. 
The author discussed the propeller as a trans- 
mitter of power, the losses of efficiency due to slip 
and skin friction. He explained the design of the 
propeller on the principle that each section is an 
aerofoil traversing a helical path and deduced the 
formule for slip, pitch, thrust, speed and lost 
power, with applications to two specific cases. 
The paper was illustrated with numerous diagrams 
and full-size propeller blades. 
Revolving Cylinder Aerial Motor: KMIL BERLINER, 
Washington. : 
Under this title, the speaker described the prin- 
ciple of design and construction of a new type of 
gasoline engine for propelling aircraft. This is 
made in two sizes and so designed and built as to 
give considerable power and good running balance. 
Work of the Signal Corps in Aeronautics: G. O. 
SquigER, Signal Corps, U. S. A. 
The speaker gave a description of the work 
which has been done by the signal corps of the 
U. S. Army in the study of the prospects of the 
aeroplane for reconnaisance and dispatch work. 
A training school for members of the signal corps 
is established and a number of recruits are enrolled. 
Endowment, Grganization and Equipment of Aero- 
dynamic Laboratories: A. F. ZAHM, Washington. 
Definition, functions, scope of aeronautic and 
aerodynamic laboratories. Bearing on the deyel- 
opment of aeronautic science, art and industry. 
Endowment, organization and equipment of the 
Institut Aerodynamic de Koutchino, of the Aero- 
dynamical Laboratory of the University of Got- 
tingen, the Institute Perotechnique de St. Cyr, 
Hiffel’s Aerodynamic Laboratory, ete. Methods 
of experimentation and results obtained in various 
laboratories. Aero Club of America’s movement 
to secure the endowment of a national aeronautic 
laboratory. 
Aerial Engineering: A. LAWRENCE RotcH, Blue 
Hill Observatory. 
Vice-presidential address, published verbatwm in 
ScIENCE, January 12, 1912. 
SCIENCE 
[N.S. Vou. XXXV. No. 901 
PAPERS ON ROAD AND HIGHWAY ENGINEERING 
History of Washington Bituminous Concrete Pave- 
ments: MARTIN BROOKE, Washington. 
Bituminous concrete pavement was first laid in 
Washington in 1871, since which date over a mil- 
lion square yards have been laid. Hight hundred 
thousand square yards are still in existence, less 
than two hundred thousand yards of which are in 
the original form. Between 1871 and 1878 half a 
dozen different types of patented bituminous con- 
crete pavements were laid, a considerable portion 
of which were unsatisfactory and required resur- 
facing within a few years. The best of them, how- 
ever, were fairly durable and economical, and some 
have continued in use to this day. These pave- 
ments were characterized by their thickness and 
density and by the quality and amount of the tar 
and tar-asphalt binder used. Bituminous concrete 
was abandoned in 1878 for sheet asphalt on 
hydraulic cement base, until 1888, when the in- 
ability to obtain bids for the latter type within 
the legal limit of two dollars per square yard set 
by Congress compelled the reintroduction of bitu- 
minous concrete. The pavements of this character 
laid between 1888 and 1893 under District of 
Columbia specifications were cheaper pavements 
than the old type, and the tar distillate binder 
used was decidedly inferior to the old tar. Since 
1909, a bituminous macadam has been laid in 
suburban streets, which is very similar to the 
bituminous concrete pavement laid in the seventies. 
History of Tar Concrete Pavements in Ontario: 
W. A. McLean, Toronto. 
The first tar-concrete pavement in Ontario (Can- 
ada) was laid in Hamilton in 1880, a part of 
which is still in use. During the years 1889-1906 
numerous tar-macadam pavements were laid in 
seven cities of the province, aggregating about 25 
miles. Except in the city of Guelph, the use of 
commercial coal tar has been displaced by refined 
tar or other proprietary bitumens. The general 
experience was that for the first three years the 
surface has been satisfactory; in five years the 
surface coat, if not renewed, was worn away in 
spots; at the end of ten years the surface was 
generally rough and disintegrated, but still pro- 
tected the foundation. In Hamilton and Toronto 
the tar macadam after five or ten years has been 
protected by a wearing surface of sheet asphalt, 
from one to two inches in thickness. Hxperience 
has indicated that tar of uniform quality and of 
composition within certain range of proportions, 
while susceptible to extremes of temperature, is 
not debarred by climatic or other conditions, as 
